Directly operated, or actuated, pneumatic valves are well known in the art for controlling the flow of pressurized air therethrough. Directly operated valves may be used alone or in connection with, for example, spool valves and regulators that, in turn, control the flow of pressurized air to and from various pneumatically actuated devices such as press clutches, air brakes, sorting devices or any other pneumatic device or application requiring precise control of operating air. Two-way, three-way, four-way, and five-way direct operated valve assemblies are commonly employed in these environments. Such valves may include a valve body having a flow passage formed in the valve body. A valve member is supported within the flow passage and moveable from one position to another in direct response to an operative force placed on the valve member by an actuator. A plurality of ports are used to connect the valve assembly to a system supply pressure as well as the various active devices that the valve may control. The actuator is typically an electromagnetically operated solenoid that is energized to move the valve member to a predetermined position within the flow passage. A return spring is often employed to bias the valve member back to a known non-energized position. Valves of this type are employed in a wide variety of manufacturing environments where high flow rates and fast response times are desired.
As the technology for these valves has advanced, there has been an increase in the demand for valves designed for operating environments with ever decreasing physical dimensions. In addition, such valves must be able to operate with very fast cycle times. However, in the past, certain design barriers have limited the extent to which the size of the valve assembly could be reduced while at the same time increasing its speed. When the valve member and the flow passage are reduced below a predetermined size, the return spring may be of insufficient physical size and mechanical strength to overcome the inertia of the valve member. In addition, after the valve member has been biased in one direction by the actuator, frictional forces and surface adhesion can build up at the interface of the valve member seals and the flow passage. These frictional forces and related surface adhesion can act to inhibit movement of the valve member in the return direction which reduces valve speed and therefore increases valve response time. If the return spring is unable to provide enough biasing force to quickly or effectively move the valve member from its energized position and return it to the non-energized position when the actuator force is removed, accurate control of the active device is lost. To counter this shortcoming, various design strategies have emerged. However, the design strategies that have been proposed in the related art all suffer from the disadvantage that they add supplemental mechanisms or hardware or require a remote mounting of the valve.
For example, one design strategy proposed in the related art involves the use of dual electromagnetic actuators to move the valve members in opposite directions. Thus, the return spring is replaced by an electromagnetic actuator such as a solenoid. This solution, however, adds the complexity and cost of a second solenoid and its associated parts, and also creates another size limiting boundary. Single electromagnetic actuators that energize in both directions have also been suggested in the related art. However, these single electromagnetic actuators require a bulky double wound actuator as well as additional electronic circuitry and controls, and are therefore typically mounted in a remote location relative to the pneumatically actuated device they control. Remotely located valves defeat the goal of providing valves mounted in very close proximity to the active devices. Such valves must be interconnected via conduits or other flow passages, which require additional hardware and plumbing, and can lower pneumatic efficiencies and introduce line losses within the system.
Directly operated valves having direct mounted solenoid actuators have been developed which provide a portion of bypass flow via a bypass port in the valve member to assist the return spring in overcoming the frictional forces and related surface adhesion. An example of such a valve is provided in U.S. patent application Ser. No. 10/150,291 entitled “DIRECTLY OPERATED PNEUMATIC VALVE HAVING AN AIR ASSIST RETURN”, assigned to the assignee of the present invention, the disclosure of which is incorporated herein by reference. This bypass flow design is effective, but requires complex machining of the bypass ports which increases the cost of the valve. A need therefore exists for a further simplified directly operated valve design.